1. Field of the Invention
The present invention relates to a zoom lens, an image pickup apparatus using the same, and an information processing apparatus.
2. Description of the Related Art
In compact cameras, with narrowing of image pixels of an image pickup element, there has been increase in the number of pixels. When an attempt is made to improve a performance of an optical system to cope with narrowing of the pixel pitch, an effect of a diffraction limit becomes unignorable. In other words, a size of a light spot becomes larger than a size of a pixel. To eliminate such state, it is necessary to make an aperture of the optical system large, or in other words, to make an F-number small. While it is sought that the aperture of the optical system becomes large, it is sought that the optical system is small-size and then with a high imaging performance.
As an optical system having a comparatively large aperture, a bending variable power optical system (zoom lens system) which includes four lens groups has been disclosed in Japanese Patent Application Laid-open Publication No. 2009-216941 and Japanese Patent Application Laid-open Publication No. 2010-152143. The abovementioned bending variable power optical system includes in order from an object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power. Moreover, an optical element (prism) which bends an optical path has been disposed in the first lens group.
Here, the F-number of the optical system at a wide angle end is approximately 3.0 in the bending variable power optical system disclosed in the Japanese Patent Application Laid-open Publication No. 2009-216941, and approximately 3.4 in the bending variable power optical system disclosed in the Japanese Patent Application Laid-open Publication No. 2010-152143.